Airfoil Length Research Articles

Noise characteristic analysis and sound sources identification for rod–airfoil interaction using different subgrid-scale models

Four subgrid-scale models based on large eddy simulation (LES), such as Smagorinsky–Lilly (SL), dynamic Smagorinsky–Lilly (DSL), wall-adapting local eddy-viscosity (WALE), and dynamic kinetic-energy transport (KET) were used and couple Ffowcs Williams–Hawkings equation to accurately analyze and identify the characteristics and position of the sound sources of rod–airfoil interaction. The results of four models were compared with experimental data. It was found that the DSL model was the optimal subgrid-scale model for the study of the interaction noise considering the calculation accuracy. Therefore, the DSL model was selected for analyzing and identifying the characteristics and location of the interaction noise source. During the calculation, solid and permeable data surfaces were used for acoustic integral surfaces. The results show that the impact of the quadrupole source is negligible at a low Mach number, and the dipole noise coming from the pressure fluctuations is dominant. Meanwhile, the dipole noise from the airfoil is louder than that from the rod; the leading edge of about 30% chord length of airfoil the is the main sound source of interference effect. Above results can provide guidance for research of blade-vortex interaction noise.

Analytical Model for Ring-Wing Propulsor Thrust Augmentation

A simple, accurate, reduced-order model is developed for predicting the maximum available thrust performance of subsonic ring-wing propulsors varying in shroud airfoil length, thickness, camber, and/or angle of attack relative to the centerline. The method, applicable to drones, aircraft, ships, and more, identifies the potential upper limit to the thrust augmentation available from hover to cruise, as well as those dominant geometric features contributing to its achievement and those factors limiting its attainment. It employs classic thin airfoil aerodynamic principles and is an extension and enhancement of two previous reduced-order models. Sensitivity studies are conducted of impacts on thrust augmentation from shroud-induced viscous effects, radial loading variations induced by the propeller, and losses due to propeller-induced swirl. The model’s efficacy is assessed using over 40 independently published experimental and state-of-the-art inviscid and viscous computational data sets for more than 20 different configurations. It is shown that the model’s algebraic solutions provide very good engineering estimates at all operating conditions from hover to cruise, thereby enabling rapid preliminary design of ring-wing-based systems. Additionally, the new model provides a means to establish maps of the practical thrust augmentation limits for ring wings, providing rational starting points for formal optimization studies.

CFD Analysis of Controlling the Airflow over Airfoils using Dimples: Technical Note

The main objective of this work is to improve the aerodynamic characteristics and manoeuvrability of the aircraft. The reduction in drag and stall phenomena will automatically enhance the aerodynamic characteristics. This project is an effort to enhance the aerodynamic characteristics of airfoil by introducing surface modifications in the form of dimples. The shape of the dimples we selected is circular shaped dimple. We placed 12 dimples in both the surfaces in appropriate places so that they could delay the boundary layer formation. The dimple generally creates turbulence by creating vortices which in turn delays the boundary layer formation. With the effects of dimple, pressure drag gets reduced and also the acoustic effects get reduced. This project includes the computational analysis of dimple effect on aircraft wing using NACA 0018 symmetric airfoil with uniform cross section throughout the length of airfoil. Subsonic flows are considered for this analysis. The analyses were done under the inlet velocities of 30m/s and 60m/s at different angle of attack such as 0, 5, 10 and 15 degrees. The models were designed using CATIA V5 and simulated using ANSYS CFX software.

Strength Reliability and Parameter Sensitivity Analysis of a Missile Airfoil Structure

Abstract. In this paper, the strength reliability and parameter sensitivity analysis of a missile airfoil structure are researched. For checking strength of the missile airfoil structure before reliability analysis, stress distribution is analyzed by MSC.Nastran. Owing to the fact that machining deviation and design tolerance result in size dispersion, thickness of missile airfoil skin, thickness of ribs, length of airfoil and length of fork are considered as random variables. Based on certain analysis, the strength reliability and parameter sensitivity of the missile airfoil structure are analyzed by the fourth moment method. The reliability analysis illustrates that the strength failure probability of the missile airfoil structure is 0.01286 and the results of sensitivity reveal that the thickness of ribs is the main factor which influence on the strength reliability of airfoil structure.

Metallurgical Investigation of Defects in Super Alloy 718 Mill Forms Intended for Aerongine Applications

Abstract Super alloy 718 finds extensive utilization, particularly in aero engine industry, due to its excellent strength, low cycle fatigue and creep resistance. The alloy was manufactured using vacuum induction melting followed by vacuum arc remelting techniques. The electrodes, after thermo-mechanical processing to hot rolled square bar and flat forms, were ultrasonically inspected prior to machining of aeroengine compressor blades. During machining, crack-like defects were noticed. Visual / Stereo microscopic examination revealed that the defect was along the length of airfoil and was located at mid airfoil width. The defects were filled with dark gray colored debris. Fractographic examination of the crack facets revealed flaky gray region containing number of cracks and bright region with dimpled rupture features covered with debris. Analysis of the debris indicated the presence of oxygen in addition to the elements present in the material, suggesting that the debris is essentially an oxide. These features were correlated with processing histories and defect morphologies.

Acoustic resonances in a high-lift configuration

Low- and high-frequency acoustic resonances are computed numerically via a high-order finite-element code for a generic two-dimensional high-lift configuration with a leading-edge slat. Zero mean flow is assumed, approximating the low-Mach-number situation at aircraft landing and approach. To avoid unphysical reflections at the boundaries of the truncated computational domain, perfectly matched layer absorbing boundary conditions are implemented in the form of the complex scaling method of atomic and molecular physics. It is shown that two types of resonance exist: resonances of surface waves which scale with the total airfoil length and longitudinal cavity-type resonances which scale with the slat cove length. Minima exist in the temporal decay rate which can be associated with the slat cove resonances and depend on the slat cove geometry. All resonances are damped owing to radiation losses. However, if coherent noise sources exist, as observed in low-Reynolds-number experiments, these sources can be enhanced acoustically by the above resonances if the source frequency is close to a resonant frequency.

NPARC study of a two-dimensional transonic wall interference

An application of the inviscid (Euler) version of the NPARC code to a finite thickness airfoil inside a test section with impermeable walls is described. Three different, physically meaningful, choking patterns are generated. It is shown that, in contrast to predictions from singular perturbation analyses, the computed wind-tunnel results are not correctable to equivalent freestream conditions when flow is choked. Nomenclature A = cross-sectional area Cp = pressure coefficient CltL = upper-surface lift coefficient c = chord length of airfoil h = height of test section M = local Mach number Mch = choking Mach number Mch = choking Mach number, subsonic MS' = choking Mach number, supersonic MT = wind-tunnel Mach number M^ = Mach number imposed on outer boundary t = maximum thickness of airfoil jc = chordwise coordinate y - ratio of specific heats I. Introduction